Key advancements have been made in understanding the complexity of reactive stroma microenvironments in prostate cancer during the previous progress period. Our studies show that TGF-1 is overexpressed in prostate cancer epithelial cells and that a reactive stroma composed of myofibroblasts/carcinoma-associated fibroblasts co-evolve with cancer foci. We have shown that a reactive stroma grade 3 is predictive of prostate cancer progression. Moreover, xenograft models with engineered stroma recombined with carcinoma cells shows this stroma is tumor-promoting and TGF-1 is a key regulator of this process. The target progenitor cells of tumor-promoting reactive stroma, the process of their recruitment, and the downstream genes that transduce the tumor-promoting biology of this reactive stroma are not understood. To address this biology, we have constructed transgenic mouse lines with TGF-1 expression targeted to prostate epithelium. These mice exhibit focal stromal proliferative responses. The proposed studies are a direct extension of work in the previous period. We hypothesize that overexpression of TGF-1 in premalignant prostate cancer induces a co-evolution of a spatially associated reactive stroma that may be recruited from either local or circulating, marrow-derived progenitor cells. To address this hypothesis in detail we propose 3 Specific Aims: 1). To assess the spatial and temporal correlation between overexpression of TGF-beta and reactive stroma grades in human prostate cancer. 2). To determine the role of TGF-beta in the co-evolution of reactive stroma in prostate cancer. 3). To determine the role of TGF-beta and reactive stroma in regulating prostate cancer progression. We propose the use of novel transgenic models with recombined xenograft and in vitro approaches to address these aims. Dissecting these processes and key pathways is important for long-range studies that will focus on directed therapeutics that target the reactive stroma compartment in human prostate cancer.